Superlattice structure including two-dimensional material and device including the superlattice structure

ABSTRACT

Provided are a superlattice structure including a two-dimensional material and a device including the superlattice structure. The superlattice structure may include at least two different two-dimensional (2D) materials bonded to each other in a lateral direction, and an interfacial region of the at least two 2D materials may be strained. The superlattice structure may have a bandgap adjusted by the interfacial region that is strained. The at least two 2D materials may include first and second 2D materials. The first 2D material may have a first bandgap in an intrinsic state thereof. The second 2D material may have a second bandgap in an intrinsic state thereof. An interfacial region of the first and second 2D materials and an adjacent region may have a third bandgap between the first bandgap and the second bandgap.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/679,085, filed on Jun. 1, 2018, in the United States Patent andTrademark Office, the disclosure of which is incorporated herein in itsentirety by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under FAA9550-16-0347awarded by the Aft Force Office of Scientific Research, and by grants1420709 and 1539918 awarded by the National Science Foundation. Thegovernment has certain rights in the invention.

BACKGROUND 1. Field

The present disclosure relates to superlattice structures including atwo-dimensional material and devices including the superlatticestructure.

2. Description of Related Art

A two-dimensional (2D) material is a single-layered or half-layeredsolid material in which atoms configure crystal structures, and arepresentative example of a 2D material may include graphene. Beginningwith research on graphene, research and development have been conductedon various 2D materials having semiconductor or insulator properties.These 2D materials have been considered as next-generation materialsthat may overcome limitations on existing devices.

Recently, the research area has expanded to a technique of stackingdifferent 2D materials. A vertical heterostructure, in which differentkinds of 2D materials are stacked, may be formed easily by alayer-by-layer transfer process or a chemical vapor deposition (CVD)process, and thus, research has been actively conducted thereon.However, a lateral heterostructure, in which 2D materials are bonded ina horizontal direction, is difficult to manufacture, and there arevarious technical issues regarding the lateral heterostructure.

SUMMARY

Provided are lateral two-dimensional (2D) superlattice structures havingexcellent performance and physical properties that may be controlled.

Provided are lateral 2D superlattice structures, in which at least two2D materials are bonded in a lateral direction.

Provided are lateral 2D superlattice structures having a bandgapadjusted by a strain.

Provided are devices including the lateral 2D superlattice structure.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

According to an aspect, a lateral two-dimensional (2D) superlatticestructure includes at least two 2D materials that are different fromeach other and bonded to each other in a lateral direction. Aninterfacial region of the at least two 2D materials may be strained. Thelateral 2D superlattice structure may have a bandgap adjusted by theinterfacial region that is strained.

In some embodiments, the at least two 2D materials may include a first2D material and a second 2D material. The first 2D material may have afirst bandgap in an intrinsic state thereof. The second 2D material mayhave a second bandgap in an intrinsic state thereof. An interfacialregion of the first 2D materials and the second 2D material and anadjacent region may have a third bandgap that is between the firstbandgap and the second bandgap.

In some embodiments, the interfacial region may not include dislocationsor may include 1% or less dislocations.

In some embodiments, the interfacial region of the at least two 2Dmaterial may include 2D materials having lattice mismatch of 10% orless, and may have 10% or less strain due to the lattice mismatch.

In some embodiments, the interfacial region may have a bandgap variationrate of 30% or less with respect to one of the at least two 2Dmaterials.

In some embodiments, the at least two 2D materials may include at leasttwo transition metal dichalcogenide (TMDC) materials that are differentfrom each other.

In some embodiments, one or more of the at least two 2D materials mayinclude a metal atom among Mo, W, Nb, V, Ta, Ti, Zr, Hf, Tc, Re, Cu, Ga,In, Sn, Ge, or Pb, and a chalcogenide atom among S, Se, or Te.

In some embodiments the lateral 2D superlattice structure may have astructure, in which two kinds of 2D materials are alternately andrepeatedly arranged or three kinds of 2D materials are periodicallyarranged.

In some embodiments, lateral 2D superlattice structure may include twoor more kinds of 2D materials that are arranged to have a uniform width,a uniform ratio, or both a uniform width and a uniform ratio.

In some embodiments, the lateral 2D superlattice structure may includetwo or more kinds of 2D materials that are arranged to have differentwidths according to locations thereof, different ratios from each otheraccording to locations thereof, or both different widths and differentratios from each other according to locations thereof.

In some embodiments, the at least two 2D materials may include a first2D material and a second 2D material. A first region of the lateral 2Dsuperlattice structure may include the first 2D material and the second2D material bonded to each other at a first ratio. A second region ofthe lateral 2D superlattice structure may include the first 2D materialand the second 2D material are bonded to each other at a second ratiothat is different from the first ratio. The first region may have afirst adjusted bandgap and the second region may have a second adjustedbandgap. The second adjusted bandgap may be different from the firstadjusted bandgap.

In some embodiments, the at least two 2D materials included in thelateral 2D superlattice structure may each have a width of 1000 nm orless.

In some embodiments, the lateral 2D superlattice structure may have atriangle shape or a square shape when seen from above.

In some embodiments, the lateral 2D superlattice structure may include aP—N—P bonding structure, an N—P—N bonding structure, a P+-P—P+ bondingstructure, an N+-N—N+ bonding structure, or a combination thereof.

In some embodiments, the lateral 2D superlattice structure may include aplurality of regions having different bandgaps from one another.

According to another aspect, a two-dimensional (2D) material-containingdevice may include one of above-described the lateral 2D superlatticestructures and at least one electrode member connected to the lateral 2Dsuperlattice structure.

In some embodiments, the 2D material-containing device may include anelectronic device.

In some embodiments, the 2D material-containing device may include anoptical device.

In some embodiments, the 2D material-containing device may include atleast one of a diode type device or a transistor type device.

In some embodiments, the 2D material-containing device may furtherinclude: a first electrode element connected to a first region of thelateral 2D superlattice structure; a second electrode element connectedto a second region of the lateral 2D superlattice structure; and aconnecting element between the lateral 2D superlattice structure and thesecond electrode element for connecting the lateral 2D superlatticestructure to the second electrode element.

In some embodiments, the lateral 2D superlattice structure of the 2Dmaterial-containing device may include a plurality of first 2D materialregions and a plurality of second 2D material regions that arealternately arranged. The 2D material-containing device may furtherinclude a first electrode structure connected to the plurality of first2D material regions and a second electrode structure connected to theplurality of second 2D material regions.

In some embodiments, the 2D material-containing device may include afirst gate structure and a second gate structure. The lateral 2Dsuperlattice structure of the 2D material-containing device may includean N-channel region and a P-channel region. The first gate structure maybe on the N-channel region and the second gate structure arranged on theP-channel region.

According to an aspect, a lateral 2D superlattice structure may includea first layer having a first 2D material and a second layer having asecond 2D material. The second 2D material may be different than thefirst 2D material. The second layer may be bonded to the first layer ina lateral direction to define an interfacial region. The interfacialregion may be strained due to a lattice mismatch between the first 2Dmaterial and the second 2D material. A band gap of the interfacialregion may be between a bandgap of the first 2D material and a bandgapof the second 2D material.

In some embodiments, the lateral 2D superlattice structure may furtherinclude a plurality of first layers spaced apart from each other in thelateral direction, each having the first 2D material; and a plurality ofsecond layers spaced apart from each other in the lateral direction,each having the second 2D material. The plurality of first layers mayinclude the first layer and the plurality of second layers may includethe second layer. The plurality of first layers and the plurality ofsecond layers may be alternately or periodically arranged with eachother and concentrically arranged with each other. The plurality offirst layers and the plurality of second layers may have a same shape.The plurality of first layers and the plurality of second layers may bedifferent sizes from each other.

In some embodiments, the lateral 2D superlattice structure may furtherinclude a third layer having a third 2D material. The third layer may beconcentrically arranged between a corresponding first layer among theplurality of first layers and a corresponding second layer among theplurality of second layers. Opposite sides of the third layer may belaterally bonded to the corresponding first layer and the correspondingsecond layer. An interface between the third layer and the correspondingfirst layer may be a coherent epitaxial interface that may be straineddue to a lattice mismatch between the third 2D material and the firstmaterial. An interface between the third layer and the correspondingsecond layer may be a coherent epitaxial interface that may be straineddue to a lattice mismatch between the third 2D material and the firstmaterial.

In some embodiments, the first material may be a first transition metaldichalcogenide, the second material may be a second transition metaldichalcogenide that is different than the first transition metaldichalcogenide, and the interfacial region may include a coherentepitaxial interface between the first material and the second material.

In some embodiments, a two-dimensional (2D) material-containing devicemay include one of the above-discussed the lateral 2D superlatticestructures.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a perspective view showing processes of manufacturing alateral two-dimensional (2D) superlattice structure according to anembodiment;

FIG. 2 is a conceptual diagram illustrating coherent epitaxy, accordingto an embodiment;

FIG. 3 is a conceptual diagram illustrating incoherent epitaxy,according to a comparative example;

FIG. 4 is an annular dark-field scanning transmission electronmicroscope (ADF-STEM) image of a hetero interface and a peripheral area,according to an embodiment;

FIG. 5 shows inverse fast Fourier transformation (FFT) data of theADF-STEM image obtained from a wide region around the heterointerface ofthe superlattice structure formed according to an embodiment;

FIG. 6 is a diagram showing a selective-area electron diffraction (SAED)pattern obtained from the superlattice structure formed according to anembodiment;

FIG. 7 is an enlarged view showing some diffraction spots of FIG. 6, andis obtained as a result of the coherent heterostructure according to anembodiment;

FIG. 8 is a diagram showing diffraction spots in an incoherentheterostructure, according to a comparative example;

FIG. 9 is a scanning electron microscope (SEM) image showing lateral 2Dsuperlattice structures formed according to one or more embodiments;

FIG. 10 is a graph illustrating superlattice structures having differentratios between materials from one another, according to the embodiment;

FIG. 11 shows a false-color SEM image with respect to superlatticestructures I to V of FIG. 10;

FIG. 12 is a graph showing normalized photoluminescence (PL) spectrawith respect to WS₂ in the superlattice structures I to V of FIG. 11;

FIG. 13 is a graph showing a representative PL spectrum of WS₂/WSe₂superlattice structure according to the embodiment;

FIG. 14 is a graph showing Δ_(WS2) versus ΔW_(Se2) with respect toWS₂/WSe₂ superlattice structures having different material ratio (widthratio) from one another;

FIG. 15A is a SEM image showing a case in which a narrow WS₂ stripe isembedded in WSe₂ and FIG. 15B is a PL image showing a heterostructure ofFIG. 15A;

FIGS. 16A and 16B are PL images of WS₂/WSe₂ superlattice structures, andFIG. 16C is a PL image of an intrinsic monolayer WS₂;

FIG. 17 is a graph showing a PL spectrum of a heterostructure accordingto a comparative example;

FIG. 18 is a graph showing a PL spectrum of a heterostructure accordingto a comparative example;

FIGS. 19 to 23 are plan views of lateral 2D superlattice structuresaccording to one or more embodiments;

FIGS. 24 to 26 are plan views of lateral 2D superlattice structuresaccording to another embodiment;

FIGS. 27A and 27B are respectively a cross-sectional view and a planview of a 2D material-containing device according to an embodiment;

FIGS. 28A and 28B are respectively a cross-sectional view and a planview of a 2D material-containing device according to another embodiment;and

FIG. 29 is a cross-sectional view of a 2D material-containing deviceaccording to another embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, thepresented embodiments may have different forms and should not beconstrued as being limited to the descriptions set forth herein.Accordingly, the embodiments are merely described below, by referring tothe figures, to explain aspects. As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items. Expressions such as “at least one of,” when preceding alist of elements, modify the entire list of elements and do not modifythe individual elements of the list.

FIG. 1 is a perspective view showing processes of manufacturing alateral two-dimensional (2D) superlattice structure according to anembodiment.

Referring to FIG. 1, a first 2D material 10 is on a substrate 100, and asecond 2D material 20 may be bonded to side surfaces of the first 2Dmaterial. The first 2D material 10 and the second 2D material 20 may beseparate layers. By repeatedly performing the above process, a lateral2D superlattice structure 200 may be obtained. The lateral 2Dsuperlattice structure 200 may have a coherent heterostructure and maybe a 2D thin film that is atomically thin. A superlattice structure hasa structure, in which two or more material layers are periodicallyarranged. The coherent heterostructure may have a coherentheterointerface. The coherent heterointerface denotes a case in whichatoms of two materials are matched/bonded with one another with littleor no point defect or line defect (dislocation). On the other hand, anincoherent heterointerface or incoherent heterostructure denotes a casein which atoms of two materials are incoherent at an interface due toformation of the dislocation. In the embodiment, at least two different2D materials are bonded in a lateral direction to form a coherentheterostructure, and thus, an interfacial region of the at least two 2Dmaterials may be strained and may have a bandgap that is adjusted by thestrained interfacial region.

The first and second 2D materials 10 and 20 may be, for example,different transition metal dichalcogenides (TMDC). In this case, atleast one of the first and second 2D materials 10 and 20 may include onetransition metal selected from Mo, W, Nb, V, Ta, Ti, Zr, Hf, Tc, and Re,and one chalcogen atom selected from S, Se, and Te. The TMDC may beexpressed as, for example, MX₂, where M denotes a transition metal and Xdenotes a chalcogen atom. M may include any one of Mo, W, Nb, V, Ta, Ti,Zr, Hf, Tc, Re, etc., and X may include any one of S, Se, and Te. TheTMDC may include, for example, any one of MoS₂, MoSe₂, MoTe₂, WS₂, WSe₂,WTe₂, ZrS₂, ZrSe₂, HfS₂, HfSe₂, NbSe₂, ReSe₂, etc. However, the firstand second 2D materials 10 and 20 may include other 2D materials thanTMDC. For example, the first and second 2D materials 10 and 20 mayinclude chalcogenide materials including non-transition metal. Thenon-transition metal may include, for example, any one of Ga, In, Sn,Ge, Pb, etc. That is, a compound of the non-transition metal such as anyone of Ga, In, Sn, Ge, Pb, etc. and the chalcogenide atom such as S, Se,and Te may be used as the first and second 2D materials 10 and 20. Thechalcogenide material including the non-transition metal may include,for example, any one of SnSe₂, GaS, GaSe, GaTe, GeSe, In₂Se₃, InSnS₂,etc. Therefore, at least one of the first and second 2D materials 10 and20 may include one metal atom selected from Mo, W, Nb, V, Ta, Ti, Zr,Hf, Tc, Re, Cu, Ga, In, Sn, Ge, and Pb and one chalcogenide atomselected from S, Se, and Te. However, materials (atoms) suggested hereinare examples, and other materials (atoms) may be used.

The lateral 2D superlattice structure 200 may be formed by a modulatedchemical vapor deposition (CVD) process. The modulated CVD process maybe a modulated metal-organic CVD (MOCVD) process. In this case, sourcematerials (precursor materials) of the first and second 2D materials 10and 20 are alternately injected into a reaction chamber, andconcentration and injection time thereof may be independently andprecisely controlled. For example, a first chalcogen precursor for thefirst 2D material 10 and a second chalcogen precursor for the second 2Dmaterial 20 may be alternately injected while constantly injecting adesired (and/or alternatively predetermined) metal precursor materialinto the reaction chamber. Here, a time period for injecting the firstchalcogen precursor and a time period for injecting the second chalcogenprecursor may be controlled. When the first 2D material 10 is WS₂ andthe second 2D material 20 is WSe₂, WS₂ and WSe₂ may grow in proportionto growth time (reaction time) thereof, but WS₂ may grow two timesfaster than WSe₂ with respect to the same growth time (reaction time).In addition, a flow rate of the precursor, an injection amount of acarrier gas, a reaction temperature, and pressure may be controlled. Forexample, during a synthesis of the lateral 2D superlattice structure200, a growth environment may be constantly maintained regardless of aspecific TMDC composition. When the first 2D material 10 includes afirst TMDC and the second 2D material 20 includes a second TMDC that isdifferent from the first TMDC, during the formation of the first andsecond TMDCs, a temperature, a pressure, an overall flow rate, etc. maybe constantly maintained except for a difference of the chalcogenprecursors. According to an embodiment, each of the first and second 2Dmaterials 10 and 20 may grow at a relatively slow growth rate that isclose to a thermodynamic equilibrium. For example, the growth rate maybe about 20 nm/min to about 60 nm/min. As such, the interface betweenthe first and second 2D materials 10 and 20 may have a straightheterointerface having W-zigzag edges that are generally stabilized. Adimension (width) of each first 2D material 10 and a dimension (width)of each second 2D material 20 may be controlled by optimizing processingconditions and precisely controlling the processing conditions, andthus, generation of dislocation between the first and second 2Dmaterials may be prevented or restrained (e.g., minimized).

FIG. 2 is a conceptual diagram (plan view) for illustrating coherentepitaxy, according to an embodiment.

FIG. 2 shows a concept of the coherent epitaxy. A first 2D material 1Aand a second 2D material 2A may be bonded to each other to form acoherent heterointerface. As such, for example, a coherent monolayerTMDC superlattice structure may be obtained. The coherent monolayer TMDCsuperlattice structure may entirely have a crystallized structure. Aninterfacial region between the first 2D material 1A and the second 2Dmaterial 2A may not include dislocation or may include dislocation byabout 1% or less. Here, % may denote atomic %. The dislocations mayexist or may not substantially exist within about 1% of atoms at theinterfacial region. Also, the interfacial region may have a pointdefect, little or no other defect. By forming the coherentheterointerface as described above, the interfacial region between thefirst and second 2D materials 1A and 2A and peripheral first and second2D materials 1A and 2A are strained, and thus, may have an adjustedbandgap. In an intrinsic state of the first 2D material 1A and anintrinsic state of the second 2D material 2A, lattice mismatch thereofmay be within about 10% or about 5%. Since they are coherently bonded,strain of about 10% or about 5% or less may be caused due to the latticemismatch at the interfacial region thereof. When the first 2D material1A has a first bandgap in the intrinsic state thereof and the second 2Dmaterial 2A has a second bandgap in the intrinsic state thereof, theinterfacial region therebetween and the peripheral region may have athird bandgap that is between the first bandgap and the second bandgap.The interfacial region may have a bandgap variation rate of about 30% orless with respect to one of the two 2D materials 1A and 2A. In FIG. 2,a_(//) denotes a lattice constant in a direction parallel with theheterointerface and a_(⊥) denotes a lattice constant in a directionperpendicular to the heterointerface.

FIG. 3 is a conceptual diagram (plan view) for illustrating incoherentepitaxy, according to a comparative example.

FIG. 3 shows a concept of the incoherent epitaxy. A first 2D material 1Band a second 2D material 2B may form an incoherent heterointerface. Dueto the lattice mismatch between two different kinds of 2D materials 1Band 2B, point defects and line defects (dislocation) are generated onthe interface thereof and a strain is not substantially caused. Also,the first 2D material 1B exhibits optical characteristics that come froman intrinsic bandgap thereof, and the second 2D material 2B exhibitsoptical characteristics that come from an intrinsic bandgap thereof. Theoptical characteristics of the two 2D materials 1B and 2B overlap eachother on the interfacial region thereof. That is, independent physicalproperty is shown in a region of each of the 2D materials 1B and 2B, andoverlapped physical properties are shown in the interfacial region.Therefore, a bandgap tuning effect may not be obtained. In FIG. 3, a₁and a₂ respectively denote lattice constants in a direction parallelwith the heterointerface of the first 2D material 1B and the second 2Dmaterial 2B.

FIG. 4 is an annular dark-field scanning transmission electronmicroscope (ADF-STEM) image of a heterointerface (dashed line) and aperipheral area, according to an embodiment. The superlattice structureof FIG. 4 has a WS₂/WSe₂ bonding structure.

Referring to FIG. 4, the superlattice structure may maintain the latticecoherence throughout the entire region, and may not substantiallyinclude a misfit dislocation. An arrow in FIG. 4 denotes an epitaxydirection, which is also applied to FIGS. 5 to 8.

FIG. 5 shows inverse fast Fourier transformation (FFT) data of theADF-STEM image obtained from a wide region around the heterointerface ofthe superlattice structure formed according to an embodiment. Aninserted view at an upper left side of FIG. 5 shows spots of the FFT,and the data is obtained based on circled spots.

Referring to FIG. 5, it may be identified that atoms form continuouslines without a misfit dislocation around the heterointerface over alarge area.

FIG. 6 shows a selective-area electron diffraction (SAED) patternobtained from the superlattice structure formed according to anembodiment. The data is obtained from a region having a diameter of 280nm.

Referring to FIG. 6, a single-crystal-like that is sharp and hasisotropic diffraction spots is shown.

FIG. 7 is an enlarged view showing some diffraction spots of FIG. 6, andis obtained as a result of the coherent heterostructure according to anembodiment. FIG. 7 shows an enlarged view of spots in circles andsquares of FIG. 6.

Referring to FIG. 7, diffraction data (in circles) corresponding to thedirection in parallel with the heterointerface shows a singlediffraction spot without separation. This denotes that a completelattice matching is made in the direction parallel with theheterointerface. That is, it may denote δ_(//)=0. The diffraction data(in squares) corresponding to a direction perpendicular to theheterointerface shows similar lattice constants. Although two spots,that is, spots respectively induced from WS₂ and WSe₂, the mismatch(δ_(⊥)) was very small, that is, 1.2%. This is very small compared withthe lattice mismatch between the two materials, that is, about 4%.

FIG. 8 shows diffraction spots in an incoherent heterostructure,according to a comparative example. Measurement conditions of FIG. 8 arethe same as those of FIG. 7. Results shown in FIG. 8 are obtained fromthe incoherent WS₂/WSe₂ heterostructure.

Referring to FIG. 8, there was found lattice mismatch of about 4% in thedirection parallel with and the direction perpendicular to theheterointerface.

FIG. 9 is a scanning electron microscope (SEM) image showing lateral 2Dsuperlattice structures formed according to one or more embodiments.

Referring to FIG. 9, monolayer WS₂/WSe₂ superlattice structures areshown. Here, regions that are relatively dark denote WS₂ and region thatare relatively bright denote WSe₂. According to forming conditions, awidth of each of 2D material regions may be controlled. The width ofeach of 2D materials forming the superlattice structure may be about1000 nm or less. A triangle unit of each of WS₂ and WSe₂ may have anequilateral triangle shape having a high symmetric property and evenwidth. As the coherent heterointerface is formed, the symmetricity anduniformity of each triangle unit may be greatly improved.

FIG. 9 illustrates the WS₂/WSe₂ superlattice structure as an example,but the materials may vary. For example, in some embodiments, MoS₂ maybe further formed between WSe₂ and WS₂, and the materials may variouslychange. The lateral 2D superlattice structure according to an embodimentmay have a structure, in which two kinds of 2D materials are alternatelyand repeatedly arranged or three or more 2D materials are periodicallyarranged.

According to embodiments, an induced strain may vary depending on widthsand/or a ratio between two or more kinds of 2D materials configuring thelateral 2D superlattice structure, and accordingly, a bandgap tuningeffect may also change.

FIG. 10 is a graph illustrating superlattice structures having differentratios between materials from one another, according to an embodiment.

Referring to FIG. 10, WS₂/WSe₂ superlattice structures I to V wereformed while varying a width of WS₂ (a width in a directionperpendicular to the interface) and a width of WSe₂ (a widthperpendicular to the interface). Here, numerical values in parenthesesdenote a ratio (ρ) between the width of WS₂ (d_(WS2)) and the width ofWSe₂ (d_(WSe2)), that is, d_(WS2)/d_(WSe2). As d_(WSe2) decreases ord_(WSe2) increases, that is, as the ratio (ρ) decreases, a tensilestrain increases in WS₂ and a compressive strain may decrease in WSe₂,and the lattice constant in the horizontal direction and the latticeconstant in the vertical direction with respect to WS₂ may be closer tointrinsic values. Additionally, band structures of both WS₂ and WSe₂ maybe adjusted by the applied strain, and a size of a direct bandgap may bereduced due to the tensile strain and may be increased due to thecompressive strain. The band structure depending upon the strain mayallow a broad tuning of optical characteristics to be possible by thesuperlattice design.

FIG. 11 shows a false-color SEM image with respect to the superlatticestructures I to V of FIG. 10.

Referring to FIG. 11, in the superlattice structures I to V, dark (e.g.,blue) color represents WS₂ and light (e.g., yellow) color representsWSe₂. The superlattice structures I to V are coherent heterostructuresand have different ratio (ρ) of materials from one another (see FIG.10).

FIG. 12 is a graph showing normalized photoluminescence (PL) spectrawith respect to WS₂ in the superlattice structures I to V of FIG. 11.Also, FIG. 12 also shows normalized PL spectrum with respect tointrinsic WS₂.

Referring to FIG. 12, the normalized WS₂ peak shifts to a left side fromthe structure I towards the structure V. As the ratio (ρ) between thematerials decreases, the normalized WS₂ peak may be away from theintrinsic WS₂ peak. The normalized WS₂ peak may correspond to thebandgap.

FIG. 13 is a graph showing a representative PL spectrum of the WS₂/WSe₂superlattice structure according to an embodiment.

Referring to FIG. 13, the WS₂ peak may be shifted from 1.97 eV, that is,the intrinsic peak energy, to a left side by Δ_(WS2) (that is,red-shifted), and the WSe₂ peak may be shifted from 1.61 eV, that is,the intrinsic peak energy, to a right side by Δ_(WSe2) (that is,blue-shifted). Therefore, WS₂ and WSe₂ regions may have adjustedbandgaps.

FIG. 14 is a graph showing Δ_(WS2) versus Δ_(WSe2) with respect toWS₂/WSe₂ superlattice structures having different material ratio (widthratio) from one another.

Referring to FIG. 14, Δ_(WSe2) tends to decrease as Δ_(WS2) increases.When Δ_(WS2) and Δ_(WSe2) both have positive values, it denotes that WS₂is subjected to tensile deformation and WSe₂ is subjected to compressivedeformation.

FIG. 15A is a SEM image showing a case in which a narrow WS₂ stripe isembedded in WSe₂ and FIG. 15B is a PL image showing a heterostructure ofFIG. 15A. The PL image of FIG. 15B is obtained from photon energy of1.75 eV.

Referring to FIGS. 15A and 15B, it may be identified that a highlyred-shifted WS₂ PL peak is generated from a strained WS₂ region.

FIGS. 16A and 16B are PL images of WS₂/WSe₂ superlattice structures, andFIG. 16C is a PL image of an intrinsic monolayer WS₂. FIGS. 16A and 16Bare obtained from photon energy close to the WS₂ of the correspondingsuperlattice structures, that is, FIG. 16A is obtained at 1.82 eV andFIG. 16B is obtained at 1.91 eV. FIG. 16C is obtained at photon energyof 2.00 eV.

Referring to FIG. 16, the superlattice structures of FIGS. 16A and 16Beach have a supercell dimension smaller than a diffraction limit, and inthis case, the superlattice structures show uniform PL intensity at eachpeak throughout the entire structure, similarly to the intrinsic WS₂ ofFIG. 16C. Here, the supercell denotes a pair of 2D materials bonded toeach other.

Strong epitaxial strains may be precisely engineered by the supercelldimension of nano-scale. The superlattice structure having engineeredstrain may be obtained by the superlattice design. Physical propertiesof the superlattice structure may be precisely controlled due to theengineered strain. In some cases, the superlattice structure accordingto embodiments may exhibit characteristics of a new material, ratherthan independent characteristics of a plurality of 2D materials. Inother words, the bandgap tuning characteristics may be implemented inentire 2D superlattice structure. The 2D superlattice structure having adesired bandgap may be formed by using a plurality of different 2Dmaterials. Also, by suppressing occurrence of defect at the interface, ahigh level of electrical characteristics may be ensured.

According to an embodiment, the first 2D material forming thesuperlattice structure may have a first bandgap in an intrinsic statethereof, the second 2D material may have a second bandgap in anintrinsic state thereof, the first 2D material region adjacent to aninterface between the first and second 2D materials may have a thirdbandgap, and the second 2D material region adjacent to the interface mayhave a fourth bandgap. Here, the third and fourth bandgaps may existbetween the first bandgap and the second bandgap. When a size of thesupercell included in the superlattice structure is small, e.g., tens ofnm, the superlattice structure may entirely have an adjusted bandgap.

FIG. 17 is a graph showing a PL spectrum of a heterostructure accordingto a comparative example. The heterostructure according to thecomparative example has a MoS₂/MoSe₂ structure, and an interface is anincoherent heterointerface.

Referring to FIG. 17, intrinsic characteristics of MoS₂ are shown in theMoS₂ region, intrinsic characteristics of MoSe₂ are shown in the MoSe₂region, and characteristics of MoS₂ and MoSe₂ are shown together in thebonded portion (interface) thereof. In this structure, the physicalproperties of each material are independently shown in each materialregion, and the bandgap tuning effect is not obtained.

FIG. 18 is a graph showing a PL spectrum of a heterostructure accordingto a comparative example. The heterostructure according to thecomparative example has a WSe₂/MoS₂ structure, and an interface is anincoherent heterointerface.

Referring to FIG. 18, intrinsic characteristics of WSe₂ are shown in theWSe₂ region, intrinsic characteristics of MoS₂ are shown in the MoS₂region, and characteristics of MoS₂ and WSe₂ are independently shown orshown together in the bonded portion (interface) thereof. In thisstructure, the bandgap tuning effect is not obtained.

The lateral 2D superlattice structure according to one or moreembodiments may have a structure, in which two or more kinds of 2Dmaterials are alternately (periodically) arranged. Here, the two or morekinds 2D materials may be arranged to have the same width and/or thesame ratio, or may be arranged to have different widths and/or differentratios according to locations thereof. In latter case, during theformation of the lateral 2D superlattice structure, the width and theratio between the 2D materials may be gradually modulated. The lateral2D superlattice structure may include a first region in which the firstand second 2D materials are bonded with a first ratio and a second ratioin which the first and second 2D materials are bonded with a secondratio that is different from the first ratio. The first region may havea first modulated bandgap and the second region may have a secondmodulated bandgap that is different from the first modulated bandgap.The lateral 2D superlattice structure according to one or moreembodiments may have a triangle or a square shape when it is seen fromabove, may include at least one bonding structure selected from P—N,P—N—P, N—P—N, P⁺—P—P⁺, and N⁺—N—N⁺, and may include a plurality ofregions having different bandgaps from one another.

FIGS. 19 to 23 are plan views of lateral 2D superlattice structuresaccording to one or more embodiments.

In the embodiments of FIGS. 19 to 23, the 2D materials may be formedwith substantially the same widths and/or substantially the same ratio.In FIGS. 19 and 20, two kinds of 2D materials 11/21 or 12/22 arealternately arranged, and FIGS. 21 to 23, three kinds of 2D materials13/23/33, 14/24/34, or 15/25/35 are periodically arranged. The 2Dmaterials 11/21 in FIG. 19, 2D materials 12/22 in FIG. 20, 2D materials13/23/33 in FIG. 22, 2D materials 14/24/34 in FIG. 22, and 2D materials15/25/35 in FIG. 23 may be in separate layers, respectively.

FIGS. 24 to 26 are plan views of lateral 2D superlattice structuresaccording to another embodiment.

In the embodiments of FIGS. 24 to 26, 2D materials may be formed withdifferent widths and/or different ratio according to locations thereof.In FIGS. 24 to 26, two kinds of 2D materials 16/26, 17/27, or 18/28 arealternately arranged, and a width of each 2D material may graduallyincrease or decrease. Although not shown in the drawings, three or morekinds of 2D materials may be arranged while varying widths thereof. The2D materials 16/26 in FIG. 24, 2D materials 17/27 in FIG. 25, and 2Dmaterials 18/28 in FIG. 26 may be in separate layers, respectively.

The lateral 2D superlattice structure according to embodiments may beeffectively applied to various electronic devices and optical devices. A2D material-containing device according to an embodiment may include thelateral 2D superlattice structure described above and at least oneelectrode member connected to the lateral 2D superlattice structure.Also, the 2D material-containing device may include at least one of adiode type device and a transistor type device. Hereinafter, the 2Dmaterial-containing device according to an embodiment will be describedbelow with reference to FIGS. 27 to 29.

FIGS. 27A and 27B are respectively a cross-sectional view and a planview of a 2D material-containing device according to an embodiment.

Referring to FIGS. 27A and 27B, a lateral 2D superlattice structure S10according to an embodiment may be arranged on a substrate SUB10. Thelateral 2D superlattice structure S10 may have a structure, in which afirst 2D material M10 and a second 2D material M20 are alternatelybonded. The 2D material-containing device may further include a firstelectrode element E10 connected to the first region of the lateral 2Dsuperlattice structure S10 and a second electrode element E20 connectedto the second region of the lateral 2D superlattice structure S10. Aconnecting element C10 may be further provided between the lateral 2Dsuperlattice structure S10 and the second electrode element E20 forconnecting the lateral 2D superlattice structure S10 to the secondelectrode element E20. The connecting element C10 may include aconductive layer or a semiconductor layer, and may be transparent.

FIGS. 28A and 28B are respectively a cross-sectional view and a planview of a 2D material-containing device according to another embodiment.

Referring to FIGS. 28A and 28B, a lateral 2D superlattice structure S11may be provided on a substrate SUB11. The lateral 2D superlatticestructure S11 may include a plurality of first and second 2D materialregions M11 and M12 that are alternately arranged. A plurality of firstunit electrodes E11 may be connected to the plurality of first 2Dmaterial regions M11 and a first common electrode E110 may be connectedto the plurality of first unit electrodes E11. The plurality of firstunit electrodes E11 and the first common electrode E110 may configure afirst electrode structure. A plurality of second unit electrodes E21 maybe connected to the plurality of second 2D material regions M21 and asecond common electrode E210 may be connected to the plurality of secondunit electrodes E21. The plurality of second unit electrodes E21 and thesecond common electrode E210 may configure a second electrode structure.

The device described above with reference to FIGS. 27A to 28B mayinclude the superlattice structures S10 and S11 including a P—N diodestructure having the tuned bandgap, and may be used as a photodiode or alight-emitting device. The optical characteristics/performances of thedevice may be modulated and improved through the bandgap tuning.

FIG. 29 is a cross-sectional view of a 2D material-containing deviceaccording to another embodiment.

Referring to FIG. 29, a lateral 2D superlattice structure S12 accordingto an embodiment may be arranged on a substrate SUB12. The lateral 2Dsuperlattice structure S12 may have a structure, in which a first 2Dmaterial M12 and a second 2D material M22 are alternately arranged. Thelateral 2D superlattice structure S12 may include at least one selectedfrom P—N—P, N—P—N, P⁺—P—P⁺, and N⁺—N—N⁺ bonding structures.

A first gate electrode G12 may be provided on a region corresponding toa first channel region C1, from among the plurality of first 2Dmaterials M12. A first gate insulating layer N12 may be arranged betweenthe first channel region C1 and the first gate electrode G12. A firstsidewall insulating layer SP1 may be arranged on opposite sides of thefirst gate electrode G12. Also, first and second electrode elements E12and E13 may be further provided on the superlattice structures S12 atopposite sides of the first channel region C1. One of the first andsecond electrode elements E12 and E13 may be a source electrode and theother may be a drain electrode.

A second gate electrode G22 may be provided on a region corresponding toa second channel region C2, from among the plurality of second 2Dmaterials M22. A second gate insulating layer N22 may be arrangedbetween the second channel region C2 and the second gate electrode G22.A second sidewall insulating layer SP2 may be arranged on opposite sidesof the second gate electrode G22. Also, third and fourth electrodeelements E22 and E33 may be further provided on the superlatticestructures S12 at opposite sides of the second channel region C2. One ofthe third and fourth electrode elements E22 and E23 may be a sourceelectrode and the other may be a drain electrode. When one of the firstand second channel regions C1 and C2 is an N-channel region and theother is a P-channel region, the device according to an embodiment maybe a complementary metal oxide semiconductor (CMOS) type device.However, in some embodiments, the device is not limited to a CMOS typedevice. Transistors may be configured on channel regions of the sametype. Other various modifications may be allowed.

The device described with reference to FIG. 29 may be a field effecttransistor (FET) type device. A mobility of a carrier (electron or hole)of the channel regions C1 and C2 in the device may be improved due to astrain effect. Therefore, the device may have excellent performances.

In embodiments, the lateral 2D superlattice structure may be applied tovarious optical devices such as an optoelectronic devices,photodetectors, photovoltaic devices, phototransistors, and photodiodes, and may be also applied to various electronic devices using thetransistor or diode structure. In addition, in embodiments, the lateral2D superlattice structure may be applied to various devices.

According to the embodiments, the lateral 2D superlattice structurehaving excellent performances and physical properties that are easilycontrolled, and the lateral 2D superlattice structure in which at leasttwo 2D materials bonded to each other in a lateral direction may beimplemented. A lateral 2D superlattice structures having a bandgapadjusted by a strain may be implemented. Various devices (electronicdevice/optical device) having excellent performances may be implementedby applying the lateral 2D superlattice structure thereto.

In the specification, many details are described in detail, but they arenot provided to limit the scope of the disclosure, and should beinterpreted as illustrating the embodiment. For example, one of ordinaryskill in the art would appreciate that the configuration of the lateral2D superlattice structure described above with reference to FIGS. 1, 2,4 to 7, 9 to 16, and 19 to 26 may be variously modified. In detail, atleast a part of the lateral 2D superlattice structure may have amulti-layer structure, not the monolayer (mono atomic layer), and inthis case, general characteristics of the 2D material may be maintained.Also, material composition and entire shape of the superlatticestructure may be variously modified. Also, a predetermined dopantmaterial may be further added to the superlattice structure. Inaddition, the configuration of the device described above with referenceto FIGS. 27A to 29 is an example, but the device to which thesuperlattice structure is applied may be variously modified. Thus, thescope of the disclosure should be determined by the technical idea setforth in the claims, not by the embodiments.

It should be understood that embodiments described herein should beconsidered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould typically be considered as available for other similar featuresor aspects in other embodiments. While one or more embodiments have beendescribed with reference to the figures, it will be understood by thoseof ordinary skill in the art that various changes in form and detailsmay be made therein without departing from the spirit and scope asdefined by the following claims.

What is claimed is:
 1. A lateral two-dimensional (2D) superlatticestructure, comprising: at least two 2D materials that are different fromeach other and coherently bonded to each other in a lateral direction,an interfacial region of the at least two 2D materials being strained,the lateral 2D superlattice structure having a bandgap adjusted by theinterfacial region that is strained such that a bandgap of theinterfacial region is between a between a first bandgap of a first 2Dmaterial and a second bandgap of a second 2D material among the at leasttwo 2D materials that are different from each other, the first 2Dmaterial and the second 2D material being coherently bonded to eachother at the interfacial region, wherein the first 2D material is afirst 2D transition metal dichalcogenide (TMDC) material, the second 2Dmaterial is a second 2D TMDC material, the first 2D TMDC material hasthe first bandgap in an intrinsic state thereof, the second 2D TMDCmaterial has the second bandgap in an intrinsic state thereof, the first2D TMDC material and the second 2D TMDC material have a same transitionmetal element or a same chalcogen element, and the bandgap of theinterfacial region and an adjacent region have a third bandgap that isbetween the first bandgap and the second bandgap.
 2. The lateral 2Dsuperlattice structure of claim 1, wherein the interfacial region doesnot include dislocations or includes 1% or less dislocations.
 3. Thelateral 2D superlattice structure of claim 1, wherein the interfacialregion of the at least two 2D materials has a lattice mismatch of 10% orless and has 10% or less strain due to the lattice mismatch.
 4. Thelateral 2D superlattice structure of claim 1, wherein the interfacialregion has a bandgap variation rate of 30% or less with respect to oneof the at least two 2D materials.
 5. The lateral 2D superlatticestructure of claim 1, wherein one or more of the at least two 2Dmaterials include a metal atom among Mo, W, Nb, V, Ta, Ti, Zr, Hf, Tc,Re, Cu, Ga, In, Sn, Ge, or Pb, and a chalcogenide atom among S, Se, orTe.
 6. The lateral 2D superlattice structure of claim 1, wherein thelateral 2D superlattice structure has a structure, in which two kinds of2D materials are alternately and repeatedly arranged or three kinds of2D materials are periodically arranged.
 7. The lateral 2D superlatticestructure of claim 1, wherein the lateral 2D superlattice structure hastwo or more kinds of 2D materials that are arranged to have a uniformwidth, a uniform ratio, or both a uniform width and a uniform ratio. 8.The lateral 2D superlattice structure of claim 1, wherein the lateral 2Dsuperlattice structure includes two or more kinds of 2D materials thatare arranged to have different widths in the lateral direction accordingto locations thereof, different width ratios in the lateral directionfrom each other according to locations thereof, or both different widthsin the lateral direction and different width ratios in the lateraldirection from each other according to locations thereof.
 9. The lateral2D superlattice structure of claim 1, wherein the at least two 2Dmaterials included in the lateral 2D superlattice structure each have awidth of 1000 nm or less.
 10. The lateral 2D superlattice structure ofclaim 1, wherein the lateral 2D superlattice structure has a triangleshape or a square shape when seen from above.
 11. The lateral 2Dsuperlattice structure of claim 1, wherein the lateral 2D superlatticestructure includes a P—N—P bonding structure, an N—P—N bondingstructure, a P⁺—P—P⁺ bonding structure, an N⁺—N—N⁺ bonding structure, ora combination thereof.
 12. The lateral 2D superlattice structure ofclaim 1, wherein the lateral 2D superlattice structure includes aplurality of regions having different bandgaps from one another.
 13. Atwo-dimensional (2D) material-containing device, comprising: the lateral2D superlattice structure of claim 1; and at least one electrode memberconnected to the lateral 2D superlattice structure.
 14. The 2Dmaterial-containing device of claim 13, wherein the 2Dmaterial-containing device includes an electronic device.
 15. The 2Dmaterial-containing device of claim 13, wherein the 2Dmaterial-containing device includes an optical device.
 16. The 2Dmaterial-containing device of claim 13, wherein the 2Dmaterial-containing device includes at least one of a diode type deviceor a transistor type device.
 17. The 2D material-containing device ofclaim 13, wherein the lateral 2D superlattice structure includes aplurality of first 2D material regions and a plurality of second 2Dmaterial regions that are alternately arranged, the 2Dmaterial-containing device further includes a first electrode structureconnected to the plurality of first 2D material regions, and the 2Dmaterial-containing device further includes a second electrode structureconnected to the plurality of second 2D material regions.
 18. The 2Dmaterial-containing device of claim 13, further comprising: a first gatestructure; and the lateral 2D superlattice structure includes anN-channel region and a P-channel region, and the first gate structure ison the N-channel region, and the second gate structure is on theP-channel region.
 19. A two-dimensional (2D) superlattice structure,comprising: at least two 2D materials that are different from each otherand bonded to each other in a lateral direction, an interfacial regionof the at least two 2D materials being strained, the lateral 2Dsuperlattice structure having a bandgap adjusted by the interfacialregion that is strained, wherein the at least two 2D materials include afirst 2D material and a second 2D material, a first region of thelateral 2D superlattice structure includes the first 2D material and thesecond 2D material bonded to each other at a first width ratio in thelateral direction, a second region of the lateral 2D superlatticestructure includes the first 2D material and the second 2D materialbonded to each other at a second width ratio in the lateral directionthat is different from the first width ratio in the lateral direction,the first region has a first adjusted bandgap, and the second region hasa second adjusted bandgap that is different from the first adjustedbandgap.
 20. A two-dimensional (2D) material-containing device,comprising: a lateral two-dimensional (2D) superlattice structureincluding at least two 2D materials that are different from each otherand bonded to each other in a lateral direction, an interfacial regionof the at least two 2D materials being strained, the lateral 2Dsuperlattice structure having a bandgap adjusted by the interfacialregion that is strained; a first electrode element connected to a firstregion of the lateral 2D superlattice structure; a second electrodeelement connected to a second region of the lateral 2D superlatticestructure; and a connecting element between the lateral 2D superlatticestructure and the second electrode element for connecting the lateral 2Dsuperlattice structure to the second electrode element.